Carbon Monoxide Poisoning

Aka: Carbon Monoxide Poisoning, Carbon Monoxide

1. See Also
   1. Smoke Inhalation
   2. Carboxyhemoglobin
2. Epidemiology
   1. Emergency Department visits per year: 50,000 in U.S.
   2. Leading cause of toxin related death in United States
      1. Accidental or Intentional (Suicide) deaths per year: 5000
3. Sources: Carbon Monoxide
   1. Gas powered engine
      1. Car with faulty exhaust system
      2. Passengers riding in back of a pickup truck
      3. Swimmers at back of a houseboat
      4. Propane fueled forklifts
      5. Ice skating rink Zamboni
      6. Indoor tractor pulls
   2. Home
      1. Indoor Heaters (most common cause)
         1. Furnace
         2. Home water heaters
         3. Gas heaters
         4. Pool heaters
         5. Kerosene heaters
      2. Indoor Flames
         1. Wood stoves
         2. Indoor charcoal fires
         3. Sterno fuel
      3. Tobacco smoke
         1. Tobacco Smokers
            1. Carboxyhemoglobin levels may reach 6-10%
         2. Hookah Smokers
            1. Carboxyhemoglobin levels may reach 15-20%
         3. Nonsmokers exposed to passive smoke
            1. Cigarette tip 2.5 fold greater CO than inhaled
   3. Industrial or Occupational
      1. Steel foundry
      2. Pulp paper mill
      3. Formaldehyde and coke producing plants
      4. Fire fighters
   4. Fire
      1. Building or structure fire
      2. Wilderness fire
   5. Suicide Attempt
      1. Closed garage with car Running
      2. Ingestion of formic acid and sulfuric acid (sulphuric acid)
         1. Combination yields Carbon Monoxide
         2. Strong acid fumes may also result in Burn Injury and lung injury
         3. Swadron and Nordt (2022) EM:Rap 22(6): 5-7
4. Pathophysiology
   1. Carbon Monoxide Properties (no warning features that gas is present until symptoms develop)
      1. Colorless
      2. Odorless
      3. Non-irritating gas
      4. Small molecule that crosses through some barriers into closed spaces (e.g. drywall)
   2. Exposures leading to Toxicity
      1. Carbon Monoxide toxicity occurs at Ambient levels >200-500 parts per million
      2. More severe illness occurs with longer exposure times
   3. Carbon Monoxide inhalation
      1. Carbon Monoxide has a high affinity for Hemoglobin (>200-250 times higher affinity than oxygen)
      2. Displaces Oxygen and produces Carboxyhemoglobin
         1. Shifts oxygen dissociation curve left with poor delivery of any residual oxygen to tissues
         2. Functional Anemia is however not responsible for Carbon Monoxide's lethal effects
   4. Direct toxin effects of Carbon Monoxide
      1. Sodium channel activation
      2. Nitric oxide levels increase
      3. Neurotoxic
         1. Basal Ganglia (Parkinsonism)
         2. Occiput (occipital blindness)
         3. Frontal cortex (personality change)
   5. Inflammatory cascade (responsible for neurologic toxicity)
      1. White Blood Cell response
      2. Glutamic acid (inflammatory)
      3. Free radicals
5. History
   1. Multiple persons (e.g. family, coworkers, pets) in the same environment with similar symptoms
6. Symptoms
   1. Headache (88%)
   2. Dizziness (83%)
   3. Nausea (75%)
   4. Drowsiness (75%)
   5. Dry Mouth (44%)
   6. Syncope
   7. Chest Pain
   8. Shortness of Breath
   9. Myalgias
      1. Carbon Monoxide also binds myoglobin
7. Signs
   1. Cherry-red skin and mucosa
      1. Late or post-mortem finding
   2. Bounding Pulse
   3. Hypertension
   4. Muscular Fasciculations
   5. Stertorous breathing
   6. Dilated pupils
   7. Convulsions
   8. Altered Mental State to coma
   9. Do not rely on Oxygen Saturations (not accurate see below)
8. Findings: Carboxyhemoglobin level
   1. Carboxyhemoglobin: 10%
      1. Frontal Headache
   2. Carboxyhemoglobin: 20%
      1. Throbbing Headache
      2. Dyspnea on exertion
         1. Severe Hypoxemia requiring intubation may occur at this level
   3. Carboxyhemoglobin: 30%
      1. Impaired judgment
      2. Nausea or Vomiting
      3. Dizziness
      4. Visual disturbance
      5. Fatigue
   4. Carboxyhemoglobin: 40%
      1. Confusion
      2. Syncope
   5. Carboxyhemoglobin: 50%
      1. Coma
      2. Seizures
   6. Carboxyhemoglobin: 60%
      1. Hypotension
      2. Respiratory Failure
   7. Carboxyhemoglobin: 70%
      1. Death
9. Labs
   1. Blood grossly appears abnormal red color
   2. Venous Blood Gas
   3. Carboxyhemoglobin
      1. Normal background Carboxyhemoglobin is 2-3%
      2. Carboxyhemoglobin elevated >25% is significant and associated with toxicity
         1. See above for findings related to Carboxyhemoglobin levels
   4. Complete Blood Count
      1. Leukocytosis
10. Precautions
    1. Oxygen Saturation (Pulse Oximeter) data is inaccurate
       1. Does not distinguish Carboxyhemoglobin from oxygenated Hemoglobin
    2. Drywall does not deter Carbon Monoxide
       1. Carbon Monoxide diffuses across drywall and may permeate separated rooms in multi-tenant housing
    3. Consider concurrent Cyanide toxicity in structure fires
       1. Smoke Inhalation and Lactic Acid >8 suggests cyanide Poisoning
       2. Especially with Altered Level of Consciousness
    4. Start oxygen while awaiting lab testing results if higher level of suspicion
       1. Start 100% oxygen via non-rebreather
    5. Hyperglycemia is a Neurotoxin and worsens outcomes
       1. Consider Insulin for Glucose >300 mg/dl
11. Management: Mild Poisoning
    1. Criteria
       1. Carboxyhemoglobin <30%
       2. No Neurologic or Cardiovascular Impairment
    2. Management
       1. Oxygen 100% Non-Rebreathing Mask
          1. Continue until Carboxyhemoglobin <5%
          2. Carbon Monoxide decreases 50% in 6 hours on room air
          3. Carbon Monoxide decreases 50% in 60 minutes on Non-Rebreather Mask
          4. Carbon Monoxide decreases 50% in 30 minutes on 100% oxygen while intubated
       2. Continuous Positive Airway Pressure (CPAP) with oxygen lowers Carbon Monoxide faster than oxygen alone
          1. Bal (2020) Eur J Emerg Med 27(3):217-22 +PMID:31815874 [PubMed]
       3. Hyperbaric Oxygen Indications
          1. See Hyperbaric Oxygen below
          2. Carboxyhemoglobin >25% and associated factors (cardiac or neurologic findings, age >36 years old)
          3. Consider in Pregnancy
       4. Admission criteria
          1. All patients with Carboxyhemoglobin >25%
          2. Underlying heart disease
12. Management: Moderate Poisoning
    1. Criteria
       1. Carboxyhemoglobin: 30-40%
       2. No Neurologic Impairment
    2. Management
       1. Oxygen 100% Non-Rebreathing Mask
          1. Continue until Carboxyhemoglobin <5% (see above)
       2. Admission to telemetry (cardiovascular monitor)
       3. Consider hyperbaric oxygen (see below)
          1. Cerebellar signs
          2. Focal neurologic deficit
          3. Persistent severe Headache
          4. Loss of consciousness, Seizure or coma
          5. Glasgow Coma Scale (GCS) <15
          6. Age >36 years old
          7. Prolonged Carbon Monoxide exposure
       4. Venous Blood Gas
          1. Determine acid-base status
13. Management: Severe Poisoning
    1. Criteria
       1. Carboxyhemoglobin: >40%
       2. Neurologic Impairment
    2. Management
       1. Oxygen 100% Non-Rebreathing Mask
          1. Continue until Carboxyhemoglobin <5% (see above)
       2. Admission to telemetry (cardiovascular monitor)
       3. Endotracheal Intubation may be required due to severe Hypoxemia
       4. Venous Blood Gas
          1. Follow acid-base status
       5. Extracorporeal Membrane Oxygenation (VA-ECMO)
          1. Indicated in refractory cardiovascular collapse
       6. Hyperbaric oxygen (see below)
          1. Ideally performed within 6 hours of presentation
          2. Chamber immediately available OR
          3. No improvement in 4 hours
             1. Cardiovascular status
             2. Neurologic status
14. Management: Hyperbaric oxygen chamber
    1. Mechanism
       1. Carbon Monoxide decreases 50% in 20-30 minutes on hyperbaric oxygen at 2.8 atm
       2. Allows oxygen to dissolve in blood at a much greater extent (beyond Hemoglobin binding)
       3. Decreases inflammatory cascade
       4. Decreases reperfusion injury
    2. Efficacy
       1. Decreases risk of delayed neuropsychiatric effects
          1. Reduces risk of personality change, Parkinsonism, cognitive effects
       2. Better short-term and long-term cognitive outcome
       3. Weaver (2002) N Engl J Med 347:1057-67 [PubMed]
       4. Rose (2018) Crit Care Med 46(7): e649-55 [PubMed]
    3. Indications
       1. Carboxyhemoglobin: >40%
       2. Carboxyhemoglobin: >25-30% and associated factors
          1. Neurologic Impairment
          2. Transient or prolonged loss of consciousness
          3. Severe acidosis
          4. Cardiac involvement
          5. Abnormal neuropsychiatric findings
          6. Age >36 years old
       3. Carboxyhemoglobin: <25%
          1. Consider hyperbaric oxygen for pregnant patients
15. Complications
    1. Hypoxic Encephalopathy
       1. Cognitive effects may persist for weeks to months or even permanently (up to 15-40% of cases)
          1. Reduced risk with hyperbaric oxygen therapy (see above)
       2. Parkinsonism
       3. Occipital blindness
       4. Personality change
    2. Coronary ischemia or myocadial infarction
    3. Increased risk of Coronary Artery Disease
       1. Henry (2006) JAMA 295(4): 398-402 [PubMed]
16. Prevention
    1. Adequate Ventilation
    2. Carbon Monoxide detectors
       1. Alarm sounds when Ambient Carbon Monoxide levels are >50 parts per million
       2. Carbon Monoxide toxicity occurs at Ambient levels >200-500 parts per million
17. Resources
    1. Consumer Products Safety Commission
       1. http://www.cpsc.gov/en/safety-education/safety-education-centers/carbon-monoxide-information-center/
18. References
    1. Kinker and Glauser (2021) Crit Dec Emerg Med 35(9): 19-27
    2. Moayedi and Swaminathan in Herbert (2016) EM:Rap 16(7): 13-14
    3. Nordt and Shoenberger in Herbert (2019) EM:Rap 19(1): 4-6
    4. Reisdorf (1996) in Tintinelli (1996)
    5. (1995) MMWR Morb Mortal Wkly Rep 44:765-7 [PubMed]